From: gts (gts_2000@yahoo.com)
Date: Wed May 07 2003 - 22:37:52 MDT
I William Wiser wrote:
> So the type of fat an animal is feed affects the composition
> of it's own fat?
Yes.
> If that's true I find it interesting. I
> don't suppose you have any references handy. I can search
> but if you have any names or keywords...
Below is an abstract describing some promising research on cattle diets.
The "n-3" designation in this abstract refers to omega 3 oils and "n-6"
refers to omega 6 oils. In this study, supplementing the cattle diet with
high omega 3 linseed and fish oil had a dramatic effect on the balance of
omega 6 to 3 in cattle muscle.
We evolved on a ratio of omega 6 to 3 of about 2:1. Some even estimate the
ratio to be 1:1. The modern American diet has swung way out of balance, with
a ratio of about 10:1. Australia is even more out of balance with a ratio of
about 12:1.
This imbalance happened largely because we started feeding ourselves and our
livestock high omega 6/3 ratio grains. Grains contain little fat, but what
fat they do contain is weighted extremely in favor of omega 6 vs 3 when
compared to the natural plant foods upon which humans and animals evolved.
We feed high-carb, high-omega 6/3 ratio grains to our farm animals because
it works well for purposes of fattening them up for slaughter. We feed
ourselves more of the same and then we wonder why we're as fat as our farm
animals.
-gts
Manipulating the fatty acid composition of muscle and adipose tissue in beef
cattle.
Br J Nutr 2001 Jan;85(1):115-24 (ISSN: 0007-1145)
Scollan ND; Choi NJ; Kurt E; Fisher AV; Enser M; Wood JD
Institute of Grassland and Environmental Research, Plas Gogerddan,
Aberystwyth SY23 3EB, UK. nigel.scollan@BBSRC.ac.uk.
Enhancing the n-3 polyunsaturated fatty acid (PUFA) content of beef is
important in view of the generally saturated nature of fatty acids in
ruminant meats and the negative effect this can have on human health. This
study examined the effects of different sources of dietary n-3 PUFA on the
performance of steers and the fatty acid composition of m. longissimus
thoracis muscle and associated subcutaneous adipose tissue. Animals were fed
ad libitum on grass silage plus one of four concentrates (60:40
forage:concentrate on a DM basis) containing differing sources of lipid:
Megalac (16:0), lightly bruised whole linseed (18:3n-3), fish oil (20:5n-3
and 22:6n-3) and a mixture of linseed and fish oil (1:1, on an oil basis).
Diets were formulated so that total dietary oil intake was 6 %,
approximately half of which was from the experimental test oil. Linseed
feeding not only increased the levels of 18:3n-3 in muscle phospholipid from
9.5 to 19 mg/100 g muscle but also enhanced the synthesis of 20:5n-3, the
level of which increased from 10 to 15 mg/100 g muscle. Linseed also
increased the proportion of 18:3n-3 in muscle neutral lipid and in adipose
tissue lipids by a factor of 1.64 and 1.75 respectively. Fish oil feeding
doubled the proportion of 20:5n-3 and 22:6n-3 in muscle phospholipids. The
proportion of 18:1 trans in muscle neutral lipid was higher on the n-3 PUFA
diets than the control diet, 0.04 and 0.02 respectively. Despite the implied
modification to rumen metabolism, lipid source did not affect feed intake,
growth rate, cold carcass weight or carcass fatness, but carcass
conformation score was higher on fish oil treatments (P < 0.05). However,
total muscle fatty acid content was not different between treatments and
ranged from 3.5-4.3 % of tissue weight. The increase in n-3 PUFA in the meat
produced by feeding linseed or fish oil lowered the n-6:n-3 ratio but had
little effect on the P:S ratio.
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